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The way compatible pairs of nitrate non-utilizing mutants (nit) are selected is usually not explained and remains unclear whether these pairs are representative for an isolate or strain. In addition, tester strains of Verticillium dahliae vegetative compatibility groups (VCGs) cross-react with at least one pair of tester strains of another VCG, and although it is a common knowledge of scientists working with the fungus that reversion of nit mutants to wild type occurs far too often, this fact is rarely mentioned in papers. To overcome the above problems, a protocol was developed for the generation of large number of nit mutants from any given isolate and to ensure that compatible pairs of mutants are indeed stable and the most frequent within the putative tester mutants produced from each isolate. Thus, we provide a reproducible and objective way of selecting V. dahliae tester strains for each isolate and VCG. Although VC grouping is based on the formation of stable heterokaryons, we demonstrate in this work that cross-reactions cannot be eliminated and that strict genetic barriers between two main VCG groups are absent in V. dahliae.
The effect of gums formed in stone-fruit trees on the in vitro growth and development of Verticillium albo-atrum and V. dahliae cultured on Czapek Dox Agar (CzDA), Malt Extract Agar (MEA) and Potato Dextrose Agar (PDA) was investigated. Addition of gums at concentration 5 mg/cm3 to all used media greatly stimulated mycelium growth of V. albo-atrum and V. dahliae and sporulation of the pathogen. Surface of colony of the pathogens after 8 days of culturing on CzDA, MEA and PDA supplemented with gums increased twice on the first two media and three fold on PDA as compare to the control.
Verticillium wilt caused by Verticillium dahliae, is one of the most devastating diseases in pistachio orchards in the world including Iran. In search for an eff ective non-chemical strategy for the management of this disease, we evaluated the biocontrol potential of Trichoderma harzianum isolates obtained from the rhizosphere of healthy pistachio trees in diff erent locations of the Kerman province of Iran against V. dahliae under laboratory and greenhouse conditions. Dual culture tests in the laboratory were conducted in a completely randomized design using 72 T. harzianum isolates. Twenty isolates showed the highest in vitro antagonistic activity. Th e results indicated that all 20 isolates were capable of inhibiting the mycelial growth of V. dahliae signifi cantly. Among them, isolates Tr8 and Tr19 were the most eff ective by 88.89% and 85.12% inhibition, respectively. Extracted cell free metabolites of all eff ective isolates also inhibited the growth of V. dahliae in the culture medium signifi cantly. According to the results, isolates Tr4 and Tr6 inhibited fungal pathogen growth by 94.94% and 88.15% respectively, through production of non-volatile metabolites. In the evaluation of volatile metabolites, isolates Tr5 and Tr4 were the most eff ective by 26.27% and 24.49% growth inhibition, respectively. Based on the results of the in vitro experiments, the fi ve most eff ective isolates were selected for evaluation under greenhouse conditions for their biocontrol potential in controlling Verticillium wilt of pistachio. Results of the greenhouse, (in vivo) experiments were positive and indicated that the occurrence of wilt disease in plants treated with the antagonists alone or in combination with pathogenic fungus was lower than in plants inoculated with pathogen alone. Th e overall results of this study suggest that Trichoderma fungal antagonist may be an eff ective biocontrol agent for the control of Verticillium wilt of pistachio.
Badania prowadzono w latach 2007-2008 w Instytucie Sadownictwa i Kwiaciarstwa w Skierniewicach na polu doświadczalnym o dużej zawartości inokulum V. dahliae w glebie („pole śmierci”). Objęto nimi łącznie 35 genotypów truskawki, rosnących w 4 doświadczeniach odmianowo-porównawczych. Rośliny frigo badanych odmian wysadzano do gleby od końca kwietnia do połowy maja, zaś ocenę stopnia porażenia roślin przez werticiliozę wykonywano w odstępach miesięcznych, w okresie od sierpnia do października. Stosowano skalę bonitacyjną 0-4, w której 0 - oznacza brak symptomów choroby, 4 - bardzo silne symptomy, prowadzące do zamierania roślin. Najmniejszym porażeniem przez V. dahliae odznaczały się rośliny odmian: ‘Elkat’, ʻSenga Sengana’, ʻEvie II’, ‘Salsa’, ‘Aga’, ‘Chandler’, ‘Fara’, ‘Daroyal’, ‘Dukat’, ‘Favette’, ‘Filon’, ‘Salut’, ‘Vikat’, ‘Elianny’, ‘Albion’ i ‘Vima Rina’. ‘Elsanta’, ‘Sonata’, ‘Darselect’, ‘Camarosa’, ‘Susy’, ʻCharlotte’, 03-08-02 oraz ‘Figaro’ były w średnim stopniu porażone przez ten patogen. Najsilniej porażone były natomiast: ‘Gloria’, ‘Ventana’, ‘Vima Xima’, ‘Kent’, ‘Malling Pearl’, ‘Record’, ‘Nancy’, ‘Florin’, ‘Portola’ oraz ‘Medina’.
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